1. Field of the Invention
The present invention relates to a cooling fan, and more particularly to, a cooling fan which can reduce noises in a cooling operation in a flow system using a high static pressure by improving the structure.
2. Description of the Background Art
In general, a cooling fan is a device for preventing an apparatus from being damaged due to heat generated in the operation of the apparatus by cooling the heat. The cooling fan cools the apparatus by forcibly circulating the air by a blast force and exchanging heat between the circulated air and a heating source.
An LCD projection TV is one of the apparatuses using the cooling fan.
The LCD projection TV is an advanced audio-visual image apparatus that has been improved from a slide projector, an OHP and a full image apparatus for performing briefing or education. A computer, a camcorder, a DVD and a VTR can be connected directly to the LCD projection TV, for performing various presentations or multimedia educations by screen projection.
The cooling fan is mounted to cool heat generated by a lamp used as a light source of the projection TV.
FIG. 1 is a perspective view illustrating part of a conventional LCD projection TV using a cooling fan.
Referring to FIG. 1, the conventional LCD projection TV uses a lamp 1 having its outer circumference curved in the length direction as a light source. The lamp 1 is mounted on a lamp housing 10 to be easily replaced and handled.
High temperature heat is generated in the operation of the lamp 1. When an inside temperature of the LCD projection TV increases by the high temperature heat generated by the lamp 1, various circuits are abnormally operated. In the worst case, a circuit board is broken by overheating.
In order to solve the foregoing problem, a cooling device is disposed at the lamp housing 10, for cooling the heat generated by the lamp 1. A plurality of through holes 11 for discharging heat or exchanging heat with the open air are formed at both sides (or top and bottom surfaces) of the lamp housing 10. A cooling fan 20 for forcibly circulating the air is installed at the outer portion of the lamp housing 10, so that the air sucked through the through holes 11 formed at one side of the lamp housing 10 can efficiently exchange heat with the lamp 1.
The cooling fan 20 includes a fan 21 having a plurality of blades 23 protruded in the radial direction from an outer circumference of a hub 22 rotated by an inside motor (not shown), and a fan housing 25 having a through hole 26 formed in the thickness direction with a predetermined inside diameter, so that the fan 21 can be inserted and fixed thereto.
As illustrated in FIG. 2, in order to use the mass-produced cooling fan 20 for multipurpose, a curvature radius R1 of the curved surface of the end of the inside diameter of the inlet side contacting the lamp housing 10 and sucking the hot air generated by the lamp 1 into the fan 21 is identical to a curvature radius R2 of the curved surface of the end of the inside diameter of the outlet side externally discharging the heat absorbed air.
In the LCD projection TV using the cooling device, when the fan 21 is rotated by supplying power to the cooling fan 20 for cooling the lamp 1 that is a heating source, the air is sucked into the lamp housing 10 through the through holes 11 formed at one side of the lamp housing 10 by forcible circulation of the fan 21, absorbs the heat generated by the lamp 1, and is externally discharged from the LCD projection TV through the through hole 26 of the cooling fan 20.
Here, the cooling fan 20 must cool the lamp 1 at an optimum temperature by sufficiently circulating the air, and reduce the noises so that the user can comfortably watch the TV.
The cooling system of the LCD projection TV will now be explained. When the air is sucked through the through holes 11 of the lamp housing 10, the lamp 1 itself becomes a resistance to the air flow. In addition, the air passage is narrowed by the space occupied by the lamp 1. In order to efficiently cool the high temperature heat generated by the lamp 1 in spite of the resistance factors, the cooling fan 20 must have high static pressure and high flow rate performance.
Still referring to FIG. 2, the curvature radius R1 of the end of the inside diameter of the inlet side of the through hole 26 formed on the fan housing 25 of the cooling fan 20 is identical to the curvature radius R2 of the end of the inside diameter of the outlet side thereof. Accordingly, when the air is forcibly circulated by the cooling fan 20 and externally discharged from the TV, noises seriously increase.
FIG. 3 is a graph showing noise variations at the air inlet and outlet sides of the conventional cooling fan 20. Here, an x axis indicates a rotary frequency of the fan 21, and an y axis indicates a sound pressure level (SPL).
As shown in FIG. 3, noises N2 generated when the air is discharged to the outlet side of the cooling fan 20 are higher than noises N1 generated when the air is sucked to the inlet side of the cooling fan 20.
In addition, broad noises in a low frequency region are very high at the outlet side of the cooling fan 20. The broad noises are flow noises generated by the cooling fan 20 and have an average value of about 27 dBA, which is much larger than an average value of the noises (about 19 dBA) generated at the inlet side of the cooling fan 20. Such noises prevent the users from comfortably watching the TV.